coredump: use task comm instead of (unknown)

If we don't know the file corresponding to the binary (i.e.  exe_file is
unknown), use "task->comm (path unknown)" instead of simple "(unknown)"
as suggested by ak.

The fallback is the same as %e except it will append "(path unknown)".
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/exec.c

@@ -1657,7 +1657,7 @@ static int cn_print_exe_file(struct core_name *cn)
 
 	exe_file = get_mm_exe_file(current->mm);
 	if (!exe_file)
-		return cn_printf(cn, "(unknown)");
+		return cn_printf(cn, "%s (path unknown)", current->comm);
 
 	pathbuf = kmalloc(PATH_MAX, GFP_TEMPORARY);
 	if (!pathbuf) {